I. Field
The present invention relates generally to communication, and more specifically to techniques for efficiently using air-link resources to maintain IP connectivity for intermittently active wireless terminals.
II. Background
In an Internet Protocol (IP) network, a host communicates with another host via a router. In IP terminology, a “node” is a device that implements IP, a “router” is a node that forwards IP packets not explicitly addressed to itself, and a “host” is a node that is not a router. As used herein, “IP” generically refers to all versions of the Internet Protocol. A host may have one or multiple interfaces to a link. In IP terminology, a “link” is a communication facility or medium over which nodes can communicate at a link layer (which is the layer immediately below IP), and an “interface” is a node's attachment to a link. An interface may be viewed as a network communication port. Each interface is associated with one or more IP addresses that uniquely identify that interface.
Internet Protocol Version 6 (IPv6) is a version of Internet Protocol that is slated to replace the widely used Internet Protocol Version 4 (IPv4). IPv6 resolves some of the key limitations of IPv4. For example, IPv4 utilizes a 32-bit address that was originally thought to provide an ample number of addresses to uniquely identify machines connected to the Internet. However, the explosive growth of the Internet has created a real risk of running out of IPv4 addresses. IPv6 ameliorates this concern by utilizing a 128-bit address.
IPv6 also provides other improvements over IPv4. For example, IPv6 supports “stateless address autoconfiguration”, which is a process whereby a host can automatically configure its own IPv6 address(es). Stateless address configuration can avoid the need to manually configure each host before connection to a network, eliminate the need for a dedicated server to administer and assign addresses to hosts on the network, and facilitate renumbering of addresses for hosts on the network.
For stateless address configuration in IPv6, an IPv6 address for an interface of a host on a link is obtained by concatenating a “prefix” for the link with an interface identifier (ID) for the interface. The interface ID is a value that uniquely identifies the interface within the link and may be derived based on an identifier assigned by the interface manufacturer. The prefix may be viewed as an address for the link and is associated with a lifetime over which the prefix is valid. The host can request prefix information (i.e., the prefix and its lifetime) by sending a Router Solicitation to routers on the link. Each router would then respond by sending back a Router Advertisement with the prefix information. Each router may also periodically broadcast the prefix information to hosts on the link via Router Advertisements. Each host continually listens for Router Advertisements from the routers to obtain updated prefix information. A host can also obtain the address of each router from the Router Advertisement sent by the router. The host can send IP packets to specific routers using the router addresses.
A wireless (e.g., cellular) communication network may support voice and data services. Data communication may be achieved by using IPv6 over the air interface protocols employed by the wireless network. A wireless terminal (a host) can establish a data session with the wireless network and communicate with a network entity (a router) in order to exchange data. The terminal may be intermittently active during the data session and may enter a dormant mode when not active in order to conserve air-link resources. In the dormant mode, the data-link connection is maintained but the air-link connection is released. This allows the terminal to quickly re-establish communication whenever data needs to be sent.
Implementing stateless address autoconfiguration in a wireless network without expending too much system resources is challenging for several reasons. First, Router Advertisements may be sent at random times and less frequently for a wireless network than for a wireline network. A wireless terminal may not know when to wake up from the dormant mode to receive a Router Advertisement and may need to remain awake for a long time in order to receive the Router Advertisement. Second, the terminal is not able to send a Router Solicitation while in the dormant mode and would have to re-establish air-link connection in order to do so. Minimizing dormant reactivation is desirable to conserve air-link resources.
There is therefore a need in the art for techniques to minimize dormant reactivations to receive IPv6 Router Advertisements.